from functools import reduce
def fn(x, y):
     return x * 10 + y

def char2num(s):
     digits = {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}
     return digits[s]

L = reduce(fn, map(char2num, '13579'))
print(L)
# 13579
print("======================")

def fn(x, y):
    return x * 10 + y

print(reduce(fn, [1, 3, 5, 7, 9]))